Liquid detergents containing high levels of anionic surfactant and builder, and capable of providing superior cleaning performance, are currently on the market. Some of these compositions contain enzymes to enhance removal of enzyme-sensitive stains. The stabilization of enzymes is particularly difficult in these compositions because anionic surfactants, especially alkyl sulfates, tend to denature enzymes and render them inactive. Detergency builders can also sequester the calcium ion needed for enzyme activity and/or stability.
European Patent Application 130,756, Bott et al., published Jan. 9, 1985, discloses specific proteolytic enzymes and methods for their preparation. The enzymes of this reference are said to be useful in laundry detergents, both liquid and granular. They can be combined with surfactants (including anionics), builders, bleach and/or fluorescent whitening agents.
U.S. Pat. No. 5,030,378, Venegas, issued Jul. 9, 1991, discloses heavy duty liquid laundry detergents containing a protease referred to as "Protease A", anionic surfactant, detergency builder, and calcium ion. The compositions provide good cleaning performance, particularly through-the-wash, of enzyme-sensitive stains.
An improved proteolytic enzyme referred to as "Protease B" is described in European Patent Application Serial Number 87303761.8, filed Apr. 28, 1987, on pages 17, 24 and 98. Protease B differs from the above cited Protease A in that it has a leucine substituted for the tyrosine in position 217 on the protein backbone.
U.S. Pat. No. 4,507,219, Hughes, issued Mar. 26, 1985, discloses heavy duty liquid laundry detergents that can contain proteolytic enzyme along with anionic surfactant, saturated fatty acid, polycarboxylate builder, a neutralization system, and a solvent system. The compositions contain from 0 to about 0.04 moles of alkanolamine per 100 grams of composition. The amount of alkanolamine is minimized for best chlorine bleach compatibility.
Despite the above disclosures, it is difficult to formulate a clear, homogeneous and phase stable liquid detergent containing high levels of anionic surfactant, carboxylate builder, and enzyme. It has been found that the protease in such compositions tends to crystallize during storage, particularly after a few months or at higher temperatures. This is evidenced by the formation of a hazy product that phase separate over time. The hazy material has been determined to be crystalline protease. Thus, there is a continuing need for the development of a clear, homogeneous, and phase stable liquid detergent containing high levels of anionic surfactant, carboxylate builder, and protease.